1. Field of the Invention
The invention relates to an apparatus and the method thereof applied in a display system for adjusting the brightness of an inputted video sequence, and more particularly the apparatus of the invention is suitable for all kinds of color spaces.
2. Description of the Prior Art
Flat panel display will be the most popular display in the future, and more particularly people pay much more attention on liquid crystal display (LCD) due to the advantages including thinner thickness, lighter weight, lower radiation, higher resolution, higher brightness, and so on. Furthermore, LCD can be applied to various applications, e.g. personal computer (PC), commercial billboard, home theater, and so on.
The brightness of a conventional LCD is generated via a back light module, and the permeability of the back light module can be changed by the liquid crystal, so as to decide the brightness (luminance or gray scale level) of an image. When an 8 bit LCD is used to display images, an image has the highest brightness as the gray scale level of the image is 255, and another image has the lowest brightness as the gray scale level of the image is 0. Currently, the brightness of an LCD TV ranges between 400 cd/m2 and 600 cd/m2 as the gray scale level is 255 and between 0.7 cd/m2 and 1.4 cd/m2 as the gray scale level is 0. A pupil of the eye will automatically enlarge and shrink with the environmental brightness to control the amount of light getting into the eye. When a big area of an image is displayed with high gray levels (e.g. snow scene), the pupil will automatically shrink to reduce the amount of light getting into the eye. When a big area of an image is displayed with low gray levels (e.g. night scene), the pupil will automatically enlarge to increase the amount of light getting into the eye. In practical application, a TV program is always displayed with bright and dark image alternately, so the pupil will also enlarge and shrink at every moment when the displayed image is changed. Thus, when a user watches programs for a long time, he/she will feel tired easily due to the characteristic of high brightness of the LCD.
Referring to FIG. 1A and FIG. 1B, FIG. 1A is a diagram illustrating the relation between the brightness and the brightness ratio based on a CRT TV and an LCD TV. FIG. 1B is a diagram illustrating the relation between the lumen and the brightness ratio based on the CRT TV and the LCD TV. As shown in FIG. 1A, the product of the brightness and the brightness ratio represents the lumen outputted by the TV. As shown in FIG. 1B, when the brightness ratio is higher than a specific value, the lumen of the CRT TV will approach a constant. Accordingly, compared to the LCD TV, when a user uses the CRT TV to watch programs, the pupil of the user will not enlarge and shrink excessively, so that the user will not feel tired easily.
Moreover, when a user uses the LCD TV to watch programs for a long time, it not only causes the eye of the user heavy load but also easily causes the image bad contrast. The reason is that the pupil needs a span of time to enlarge and shrink. When the amount of light getting into the eye cannot be controlled effectively, the contrast of the image will be worse.
Therefore, the objective of the invention is to provide an apparatus and the method thereof for adjusting the brightness of an inputted video sequence, so as to solve the above-mentioned problems.